Users see this error in their Windows 2003 event log:

A worker process with process id of 'XXXX' serving application pool 'First Choice' has requested a recycle because the worker process reached its allowed processing time limit.

This is a new feature of IIS6: "Worker Process Recycling"
Details on how this all works is here:
http://www.microsoft.com/resources/documentation/iis/6/all/proddocs/en-us/ca_recycwrkrprocess.mspx

It sounds like you have IIS set to recycle after a certain time period.
So, after a certain time period, IIS resets the web app, which causes fcClient to fail.
To be honest, we haven't done any testing with Worker Process Recycling.

From reading the MS article, I would suggest trying:
1. Turn off Worker Process Recycling completely

2. If you're not a 24x7 shop, perhaps try setting it to recycle at a scheduled time, such as 3:00 AM. If you go this route, I would do some testing first to ensure that fcClient restarts properly.